• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.11a
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• pp.308-312
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• 2003

The packaging of the integrated circuits requires knowledge of ceramics and metals to accommodate the fabrication of modules that are used to construct subsystems and entire systems from extremely small components. Composite ceramics ($Al_2O_3-SiO_2$) were tested for substrates. A stress analysis was conducted for a linear work-hardening metal cylinder embedded in an infinite ceramic matrix. The bond between the metal and ceramic was established at high temperature and stresses developed during cooling to room temperature. The calculations showed that the stresses depend on the mismatch in thermal expansion, the elastic properties, and the yield strength and work hardening rate of the metal. Experimental measurements of the surface stresses have also been made on a $Cu/Al_2O_3-SiO_2$ ceramic system, using an indentation technique. A comparison revealed that the calculated stresses were appreciably larger than the measured surface stresses, indicating an important difference between the bulk and surface residual stresses. However, it was also shown that porosity in the metal could plastically expand and permit substantial dilatational relaxation of the residual stresses. Conversely it was noted that pore clusters were capable of initiating ductile rupture, by means of a plastic instability, in the presence of appreciable tri-axiality. The role of ceramics for packaging of microelectronics will continue to be extremely challenging.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.14 no.3
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• pp.115-122
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• 2004

When porous materials are dried, the particles flocculate into fish-net structure in gel phase. In order to exactly analyze the stress distribution of porous materials during drying process, the elastic tensor of microscopic gel structures has to be predicted considering pore shapes as well as porosities of porous materials. The elastic characteristics of porous materials associated with porosities were predicted analyzing microscopic gel structures with circular and cross pores via homogenization method and the drying processes of the electric porous ceramic insulator were simulated using finite element method (FEM). Comparing analysis results between consideration and negligence of pores, the deformed shape and distributions of temperature and moisture were similar but the residual stress was significantly different.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.28 no.3
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• pp.132-145
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• 2016

In case of the seabed around and under gravity structures such as submerged breakwater is exposed to a large wave action long period, the excess pore pressure will be generated significantly due to pore volume change associated with rearrangement soil grains. This effect will lead a seabed liquefaction around and under structures as a result from decrease in the effective stress. Under the seabed liquefaction occurred and developed, the possibility of structure failure will be increased eventually. In this study, to evaluate the liquefaction potential on the seabed quantitatively, numerical analysis was conducted using the expanded 2-dimensional numerical wave tank model and the finite element elasto-plastic model. Under the condition of the regular wave field, the time and spatial series of the deformation of submerged breakwater, the pore water pressure (oscillatory and residual components) and pore water pressure ratio in the seabed were estimated.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.28 no.4
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• pp.177-190
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• 2016

In case of the seabed around and under gravity structures such as submerged breakwater is exposed to a large wave action long period, the excess pore pressure will be generated significantly due to pore volume change associated with rearrangement soil grains. This effect will lead a seabed liquefaction around and under structures as a result from decrease in the effective stress. Under the seabed liquefaction occurred and developed, the possibility of structure failure will be increased eventually. Lee et al.(2016) studied for regular waves, and this study considered for irregular waves with the same numerical analysis method used for regular waves. Under the condition of the irregular wave field, the time and spatial series of the deformation of submerged breakwater, the pore water pressure (oscillatory and residual components) and pore water pressure ratio in the seabed were estimated and their results were compared with those of the regular wave field to evaluate the liquefaction potential on the seabed quantitatively. Although present results are based on a limited number of numerical simulations, one of the study's most important findings is that a more safe design can be obtainable when analyzing case with a regular wave condition corresponding to a significant wave of irregular wave.

• Geomechanics and Engineering
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• v.3 no.1
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• pp.1-16
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• 2011

Piles passing through sloping liquefiable deposits are prone to lateral loading if these deposits liquefy and flow during earthquakes. These lateral loads caused by the relative soil-pile movement will induce bending in the piles and may result in failure of the piles or excessive pile-head displacement. Whilst the weak nature of the flowing liquefied soil would suggest that only small loads would be exerted on the piles, it is known from case histories that piles do fail owing to the influence of laterally spreading soils. It will be shown, based on dynamic centrifuge test data, that dilatant behaviour of soil close to the pile is the major cause of these considerable transient lateral loads which are transferred to the pile. This paper reports the results of geotechnical centrifuge tests in which models of gently sloping liquefiable sand with pile foundations passing through them were subjected to earthquake excitation. The soil close to the pile was instrumented with pore-pressure transducers and contact stress cells in order to monitor the interaction between soil and pile and to track the soil stress state both upslope and downslope of the pile. The presence of instrumentation measuring pore-pressure and lateral stress close to the pile in the research described in this paper gives the opportunity to better study the soil stress state close to the pile and to compare the loads measured as being applied to the piles by the laterally spreading soils with those suggested by the JRA design code. This test data shows that lateral stresses much greater than one might expect from calculations based on the residual strength of liquefied soil may be applied to piles in flowing liquefied slopes owing to the dilative behaviour of the liquefied soil. It is shown at least for the particular geometry studied that the current JRA design code can be un-conservative by a factor of three for these dilation-affected transient lateral loads.

• The Journal of Engineering Geology
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• v.32 no.4
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• pp.643-659
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• 2022

Geologic sequestration technologies such as CCS (carbon capture and storage), EGS (enhanced geothermal systems), and EOR (enhanced oil recovery) have been widely implemented in recent years, prompting evaluation of the mechanical stability of storage sites. As fluid injection can stimulate mechanical instability in storage layers by perturbing the stress state and pore pressure, poroelastic models considering various injection scenarios are required. In this study, we calculate the pore pressure, stress distribution, and vertical displacement along a surface using commercial finite element software (COMSOL); fault slips are subsequently simulated using PyLith, an open-source finite element software. The displacement fields, are obtained from PyLith is transferred back to COMSOL to determine changes in coseismic stresses and surface displacements. Our sequential use of COMSOL-PyLith-COMSOL for poroelastic modeling of fluid-injection and induced-earthquakes reveals large variations of pore pressure, vertical displacement, and Coulomb failure stress change during injection periods. On the other hand, the residual stress diffuses into the remote field after injection stops. This flow pattern suggests the necessity of numerical modeling and long-term monitoring, even after injection has stopped. We found that the time at which the Coulomb failure stress reaches the critical point greatly varies with the hydraulic and poroelastic properties (e.g., permeability and Biot-Willis coefficient) of the fault and injection layer. We suggest that an understanding of the detailed physical properties of the surrounding layer is important in selecting the injection site. Our numerical results showing the surface displacement and deviatoric stress distribution with different amounts of fault slip highlight the need to test more variable fault slip scenarios.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2004.05a
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• pp.70-73
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• 2004

The packaging of the integrated circuits requires knowledge of ceramics and metals to accommodate the fabrication of modules that are used to construct subsystems and entire systems from extremely small components. Composite ceramics (Al$_2$O$_3$-SiO$_2$) were tested for substrates. A stress analysis was conducted for a linear work-hardening metal cylinder embedded in an infinite ceramic matrix. The bond between the metal and ceramic was established at high temperature and stresses developed during cooling to room temperature. The calculations showed that the stresses depend on the mismatch in thermal expansion, the elastic properties, and the yield strength and work hardening rate of the metal. Experimental measurements of the surface stresses have also been made on a Cu/Al$_2$O$_3$-SiO$_2$ceramic system, using an indentation technique. A comparison revealed that the calculated stresses were appreciably larger than the measured surface stresses, indicating an important difference between the bulk and surface residual stresses. However, it was also shown that porosity in the metal could plastically expand and permit substantial dilatational relaxation of the residual stresses. Conversely it was noted that pore clusters were capable of initiating ductile rupture, by means of a plastic instability, in the presence of appreciable tri-axiality. The role of ceramics for packaging of microelectronics will continue to be extremely challenging.

• Journal of the Korean Geotechnical Society
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• v.19 no.4
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• pp.83-93
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• 2003

This research, in order to study the effects of initial shear stress of anisotropically consolidated sand that has 0.558% fines, performed several undrained static and dynamic triaxial test. To simulate the real field conditions, loose and dense samples were prepared. Besides, the cyclic shear strength of Nakdong River sand under various combinations of initial static shear stress, stress path, pore water pressure and residual strength relationship was studied. By using Bolton's theory, peak internal friction angle at failure which has considerable effects on the relative density and mean effective stress was determined. In p'- q diagram, the phase transformation line moves closer to the failure line as the specimen's initial anistropical consolidation stress increases. Loose sands were more affected than dense sands. The increase of consolidation stress ratio from 1.4 to 1.8 had an effect on liquefaction resistance strength resulting from the increase of relativity density, and showed similar CSR values in dense specimen condition.

• Biotechnology and Bioprocess Engineering:BBE
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• v.8 no.4
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• pp.246-251
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• 2003

The blood-brain barrier (BBB) is composed of the brain capillaries, which are lined by endothelial cells displaying extremely tight intercellular junctions. Several attempts at creating an in vitro model of the BBB have been met with moderate success as brain capillary endothelial cells lose their barrier properties when isolated in cell culture. This may be due to a lack of recreation of the in vivo endothelial cellular environment in these models, including nearly constant contact with astrocyte foot processes. This work is motivated by the hypothesis that growing endothelial cells on one side of an ultra-thin, highly porous membrane and differentiating astrocyte or astrogliomal cells on the opposite side will lead to a higher degree of interaction between the two cell types and therefore to an improved model. Here we describe our initial efforts towards testing this hypothesis including a procedure for membrane fabrication and methods for culturing endothelial cells on these membranes. We have fabricated a 1 $\mu\textrm{m}$ thick, 2.0 $\mu\textrm{m}$ pore size, and 55% porous membrane with a very narrow pore size distribution from low-stress silicon nitride (SiN) utilizing techniques from the microelectronics industry. We have developed a base, acid, autoclave routine that prepares the membranes for cell culture both by cleaning residual fabrication chemicals from the surface and by increasing the hydrophilicity of the membranes (confirmed by contact angle measurements). Gelatin, fibronectin, and a 50/50 mixture of the two proteins were evaluated as potential basement membrane protein treatments prior to membrane cell seeding. All three treatments support adequate attachment and growth on the membranes compared to the control.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.26 no.6
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• pp.367-380
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• 2014

Tsunami take away life, wash houses away and bring devastation to social infrastructures such as breakwaters, bridges and ports. The targeted coastal structure object in this study can be damaged mainly by the tsunami force together with foundation ground failure due to scouring and liquefaction. The increase of excess pore water pressure composed of oscillatory and residual components may reduce effective stress and, consequently, the seabed may liquefy. If liquefaction occurs in the seabed, the structure may sink, overturn, and eventually increase the failure potential. In this study, the solitary wave was generated using 2D-NIT(Two-Dimensional Numerical Irregular wave Tank) model, and the dynamic wave pressure acting on the seabed and the estimated surface boundary of the vertical revetment. Simulation results were used as an input data in a finite element computer program(FLIP) for elasto-plastic seabed response. The time and spatial variations in excess pore water pressure, effective stress, seabed deformation, structure displacement and liquefaction potential in the seabed were estimated. From the results of the analysis, the stability of the vertical revetment was evaluated.